U.S. patent number 7,111,305 [Application Number 10/304,347] was granted by the patent office on 2006-09-19 for facilitating event notification through use of an inverse mapping structure for subset determination.
This patent grant is currently assigned to SUN Microsystems, Inc.. Invention is credited to Wei Kong, Anil Rao, Nicholas A. Solter, Ashutosh Tripathi.
United States Patent |
7,111,305 |
Solter , et al. |
September 19, 2006 |
**Please see images for:
( Certificate of Correction ) ** |
Facilitating event notification through use of an inverse mapping
structure for subset determination
Abstract
One embodiment of the present invention provides a system that
performs event notification in a distributed computing system.
During operation, the system receives an event that was generated
at a node in the distributed computing system, wherein the event
includes a set of name/value pairs associated with the event. Next,
the system compares the event against a set of client event
registrations to determine a set of clients to be notified of the
event, wherein each client event registration identifies a client
and a target set of name/value pairs, wherein the client is to be
notified of the event if the target set of name/value pairs matches
a subset of the set of name/value pairs associated with the event.
Finally, the system sends a notification of the event to the set of
clients to be notified of the event.
Inventors: |
Solter; Nicholas A. (Irvine,
CA), Kong; Wei (Fremont, CA), Rao; Anil (Sunnyvale,
CA), Tripathi; Ashutosh (Fremont, CA) |
Assignee: |
SUN Microsystems, Inc. (Santa
Clara, CA)
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Family
ID: |
46298884 |
Appl.
No.: |
10/304,347 |
Filed: |
November 26, 2002 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20040088716 A1 |
May 6, 2004 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10285176 |
Oct 31, 2002 |
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Current U.S.
Class: |
719/318 |
Current CPC
Class: |
G06F
9/542 (20130101); H04L 69/329 (20130101); H04L
67/10 (20130101) |
Current International
Class: |
G06F
9/46 (20060101) |
Field of
Search: |
;719/318 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Thomson; William
Assistant Examiner: Ho; Andy
Attorney, Agent or Firm: Park, Vaughan & Fleming LLP
Parent Case Text
RELATED APPLICATION
This application is a continuation-in-part of a pending U.S.
non-provisional patent application by inventors Ashutosh Tripathi,
Andrew L. Hisgen and Nicholas A. Solter, entitled, "Method and
Apparatus for Providing a Highly Available Distributed Event
Notification Mechanism," having Ser. No. 10/285,176, and filing
date Oct. 31, 2002. This application hereby claims priority under
35 U.S.C. 517 120 to the above-listed patent application.
Claims
What is claimed is:
1. A method for performing event notification in a distributed
computing system, comprising: receiving an event that was generated
at a node in the distributed computing system, wherein the event
includes a set of name/value pairs associated with the event;
comparing the event against a set of client event registrations to
determine a set of clients to be notified of the event, wherein
each client event registration identifies a client and a target set
of name/value pairs; wherein the client is to be notified of the
event if the target set of name/value pairs matches a subset of the
set of name/value pairs associated with the event; and sending a
notification of the event to the set of clients to be notified of
the event: wherein comparing the event against the set of client
event registrations involves performing a subset determination
operation to identify which client event registrations match a
subset of the set of name/value pairs associated with the event;
and wherein for each name/value pair associated with the event,
performing the subset determination operation involves: looking up
an entry in a hash table for the name/value pair, wherein the entry
identifies which client event registrations contain matching
name/value pairs, incrementing a counter for each client event
registration that contains a matching name/value pair, and if the
counter for a client event registration equals the number of
name/value pairs in the client event registration, adding the
associated client to the set of clients to be notified of the
event.
2. The method of claim 1, wherein prior to receiving the event, the
method further comprises initializing the hash table, which
involves: for each name/value pair in each client event
registration, creating a hash table entry for the name/value pair,
if a hash table entry for the name/value pair does not exist; and
for each name/value pair in each client event registration,
updating the hash table entry to point to the counter for the
associated client event registration; whereby a subsequent hash
table lookup for an event can increment counters for client event
registrations that contain matching name/value pairs.
3. The method of claim 1, wherein comparing the event against the
set of client event registrations additionally involves comparing a
class and a subclass associated with the event against a class and
a subclass associated with each client event registration.
4. The method of claim 1, wherein clients can include: applications
or application components running within the distributed computing
system; and applications or application components running outside
of the distributed computing system.
5. The method of claim 1, wherein the event can include: a node
joining a cluster in the distributed computing system; a node
leaving the cluster in the distributed computing system; a state
change related to an application or an application component
running within the distributed computing system; and a state change
for a group of related applications running within the distributed
computing system.
6. A computer-readable storage medium storing instructions that
when executed by a computer cause the computer to perform a method
for performing event notification in a distributed computing
system, the method comprising: receiving an event that was
generated at a node in the distributed computing system, wherein
the event includes a set of name/value pairs associated with the
event; comparing the event against a set of client event
registrations to determine a set of clients to be notified of the
event, wherein each client event registration identifies a client
and a target set of name/value pairs; wherein the client is to be
notified of the event if the target set of name/value pairs matches
a subset of the set of name/value pairs associated with the event;
and sending a notification of the event to the set of clients to be
notified of the event; wherein comparing the event against the set
of client event registrations involves performing a subset
determination operation to identify which client event
registrations match a subset of the set of name/value pairs
associated with the event; and wherein for each name/value pair
associated with the event, performing the subset determination
operation involves: looking LIP an entry in a hash table for the
name/value pair, wherein the entry identifies which client event
registrations contain matching name/value pairs, incrementing a
counter for each client event registration that contains a matching
name/value pair, and if the counter for a client event registration
equals the number of name/value pairs in the client event
registration, adding the associated client to the set of clients to
be notified of the event.
7. The computer-readable storage medium of claim 6, wherein prior
to receiving the event, the method further comprises initializing
the hash table, which involves: for each name/value pair in each
client event registration, creating a hash table entry for the
name/value pair, if a hash table entry for the name/value pair does
not exist; and for each name/value pair in each client event
registration, updating the hash table entry to point to the counter
for the associated client event registration; whereby a subsequent
hash table lookup for an event can increment counters for client
event registrations that contain matching name/value pairs.
8. The computer-readable storage medium of claim 6, wherein
comparing the event against the set of client event registrations
additionally involves comparing a class and a subclass associated
with the event against a class and a subclass associated with each
client event registration.
9. The computer-readable storage medium of claim 6, wherein clients
can include: applications or application components running within
the distributed computing system; and applications or application
components running outside of the distributed computing system.
10. The computer-readable storage medium of claim 6, wherein the
event can include: a node joining a cluster in the distributed
computing system; a node leaving the cluster in the distributed
computing system; a state change related to an application or an
application component running within the distributed computing
system; and a state change for a group of related applications
running within the distributed computing system.
11. An apparatus that performs event notification in a distributed
computing system, comprising: a receiving mechanism configured to
receive an event that was generated at a node in the distributed
computing system, wherein the event includes a set of name/value
pairs associated with the event; a comparison mechanism configured
to compare the event against a set of client event registrations to
determine a set of clients to be notified of the event, wherein
each client event registration identifies a client and a target set
of name/value pairs; wherein the client is to be notified of the
event if the target set of name/value pairs matches a subset of the
set of name/value pairs associated with the event; and a
notification mechanism configured to send a notification of the
event to the set of clients to be notified of the event; wherein
the comparison mechanism is configured to perform a subset
determination operation to identify which client event
registrations match a subset of the set of name/value pairs
associated with the event; and wherein for each name/value pair
associated with the event, the comparison mechanism is configured
to: look up an entry in a hash table for the name/value pair,
wherein the entry identifies which client event registrations
contain matching name/value pairs, increment a counter for each
client event registration that contains a matching name/value pair,
and if the counter for a client event registration equals the
number of name/value pairs in the client event registration, to add
the associated client to the set of clients to be notified of the
event.
12. The apparatus of claim 11, further comprising: a hash table
initialization mechanism; wherein for each name/value pair in each
client event registration, the hash table initialization mechanism
is configured to create a hash table entry for the name/value pair,
if a hash table entry for the name/value pair does not exist; and
wherein for each name/value pair in each client event registration,
the hash table initialization mechanism is configured to update the
hash table entry to point to the counter for the associated client
event registration; whereby a subsequent hash table lookup for an
event can increment counters for client event registrations that
contain matching name/value pairs.
13. The apparatus of claim 11, wherein the comparison mechanism is
additionally configured to compare a class and a subclass
associated with the event against a class and a subclass associated
with each client event registration.
14. The apparatus of claim 11, wherein clients can include:
applications or application components running within the
distributed computing system; and applications or application
components running outside of the distributed computing system.
15. The apparatus of claim 11, wherein the event can include: a
node joining a cluster in the distributed computing system; a node
leaving the cluster in the distributed computing system; a state
change related to an application or an application component
running within the distributed computing system; and a state change
for a group of related applications running within the distributed
computing system.
Description
BACKGROUND
1. Field of the Invention
The present invention relates to the design of distributed
computing systems. More specifically, the present invention relates
to a method and an apparatus that uses an inverse mapping structure
for subset determination to facilitate event notification in a
distributed computing system.
2. Related Art
Distributed computing systems presently make it possible to develop
distributed applications that can harness the computational power
of multiple computing nodes in performing a computational task.
This can greatly increase the speed with which the computational
task can be performed. However, it is often hard to coordinate
computational activities between application components running on
different computing nodes within the distributed computing
system.
In order to operate properly, distributed applications must somehow
keep track of the state of application components in order to
coordinate interactions between the application components. This
can involve periodically exchanging "heartbeat" messages or other
information between application components to keep track of which
application components are functioning properly.
Some distributed operating systems presently keep track of this
type of information for purposes of coordinating interactions
between operating system components running on different computing
nodes. However, these distributed operating systems only use this
information in performing specific operating system functions. They
do not make the information available to distributed applications
or other clients.
Hence, in many situations, a distributed application has to keep
track of this information on its own. Note that the additional work
involved in keeping track of this information is largely wasted
because the distributed operating system already keeps track of the
information. Moreover, the task of keeping track of this
information generates additional network traffic, which can impede
communications between nodes in the distributed computing
system.
Hence, what is needed is a method and an apparatus that enables a
distributed application to be notified of events that occur on
different computing nodes within a distributed computing system
without requiring the distributed application to perform the event
monitoring operations.
One problem in performing event notification is to rapidly
determine which clients are to be notified of an incoming event.
The naive approach is to compare the incoming event against each of
the client registrations, wherein a given client registration
identifies specific events that an associated client has registered
to be notified of. Note that this may require an incoming event to
be compared against every client registration in the system, which
can potentially be very slow.
Hence what is needed is a method and an apparatus for rapidly
determine which clients are to be notified of a specific incoming
event.
SUMMARY
One embodiment of the present invention provides a system that
performs event notification in a distributed computing system.
During operation, the system receives an event that was generated
at a node in the distributed computing system, wherein the event
includes a set of name/value pairs associated with the event. Next,
the system compares the event against a set of client event
registrations to determine a set of clients to be notified of the
event, wherein each client event registration identifies a client
and a target set of name/value pairs, wherein the client is to be
notified of the event if the target set of name/value pairs matches
a subset of the set of name/value pairs associated with the event.
Finally, the system sends a notification of the event to the set of
clients to be notified of the event.
In a variation on this embodiment, comparing the event against the
set of client event registrations involves performing a subset
determination operation to identify which client event
registrations match a subset of the set of name/value pairs
associated with the event.
In a further variation, for each name/value pair associated with
the incoming event, performing the subset determination operation
involves looking up an entry in a hash table for the name/value
pair. This entry identifies which client event registrations
contain matching name/value pairs. The system also increments a
counter for each client event registration that contains a matching
name/value pair. If the counter for a given client event
registration equals the number of name/value pairs in the client
event registration, the system adds the associated client to the
set of clients to be notified of the event. Note that the counters
are reset after each incoming event is processed.
In a variation on this embodiment, prior to receiving the event,
the system initializes the hash table. This is accomplished by
looking up a hash table entry for each name/value pair in each
client event registration, which may involve creating hash table
entries for the name/value pairs, if necessary. It also involves
updating the hash table entry to point to a counter for the
associated client event registration. In this way, a subsequent
hash table lookup for an event can increment counters for client
event registrations that contain matching name/value pairs.
In a variation on this embodiment, comparing the event against the
set of client event registrations additionally involves comparing a
class and a subclass associated with the event against a class and
a subclass associated with each client event registration.
In a variation on this embodiment, clients can include applications
or application components running within the distributed computing
system. They can also include applications or application
components running outside of the distributed computing system.
In a variation on this embodiment, the events can include cluster
membership events, such as a node joining the cluster or a node
leaving the cluster. The events can also include events related to
applications, such as a state change for an application (or an
application component), or a state change for a group of related
applications. Note that a state change for an application (or
application component) can include: the application entering an
on-line state; the application entering an off-line state; the
application entering a degraded state, wherein the application is
not functioning efficiently; and the application entering a faulted
state, wherein the application is not functioning. The events can
also include state changes related to monitoring applications or
other system components, such as "monitoring started" and
"monitoring stopped."
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 illustrates a distributed computing system in accordance
with an embodiment of the present invention.
FIG. 2 illustrates a computing node in accordance with an
embodiment of the present invention.
FIG. 3 illustrates components involved in the event forwarding
process in accordance with an embodiment of the present
invention.
FIG. 4 is a flow chart illustrating the registration process for
event notification in accordance with an embodiment of the present
invention.
FIG. 5 is a flow chart illustrating the process of forwarding an
event in accordance with an embodiment of the present
invention.
FIG. 6 illustrates various data structures that facilitate an
inverse mapping operation in accordance with an embodiment of the
present invention.
FIG. 7 presents a flow chart illustrating the process of
initializing a lookup structure for the event lookup process in
accordance with an embodiment of the present invention.
FIG. 8 presents a flow chart illustrating the event lookup process
in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION
The following description is presented to enable any person skilled
in the art to make and use the invention, and is provided in the
context of a particular application and its requirements. Various
modifications to the disclosed embodiments will be readily apparent
to those skilled in the art, and the general principles defined
herein may be applied to other embodiments and applications without
departing from the spirit and scope of the present invention. Thus,
the present invention is not intended to be limited to the
embodiments shown, but is to be accorded the widest scope
consistent with the principles and features disclosed herein.
The data structures and code described in this detailed description
are typically stored on a computer readable storage medium, which
may be any device or medium that can store code and/or data for use
by a computer system. This includes, but is not limited to,
magnetic and optical storage devices such as disk drives, magnetic
tape, CDs (compact discs) and DVDs (digital versatile discs or
digital video discs), and computer instruction signals embodied in
a transmission medium (with or without a carrier wave upon which
the signals are modulated). For example, the transmission medium
may include a communications network, such as the Internet.
Distributed Computing System
FIG. 1 illustrates a distributed computing system 100 in accordance
with an embodiment of the present invention. As is illustrated in
FIG. 1, distributed computing system 100 includes a number of
clients 121 123 coupled to a highly available server 101 through a
network 120. Network 120 can generally include any type of wire or
wireless communication channel capable of coupling together
computing nodes. This includes, but is not limited to, a local area
network, a wide area network, or a combination of networks. In one
embodiment of the present invention, network 120 includes the
Internet. Clients 121 122 can generally include any node on a
network including computational capability and including a
mechanism for communicating across the network.
Highly available server 101 can generally include any collection of
computational nodes including a mechanism for servicing requests
from a client for computational and/or data storage resources.
Moreover, highly available server 101 is configured so that it can
continue to operate even if a node within highly available server
101 fails. This can be accomplished using a failover model, wherein
if an instance of an application fails, a new instance is
automatically started, possibly on a different node within the
distributed computing system.
In the embodiment illustrated in FIG. 1, highly available server
101 includes a number of computing nodes 106 109 coupled together
through a cluster network 102. Computing nodes 106 109 can
generally include any type of computer system, including, but not
limited to, a computer system based on a microprocessor, a
mainframe computer, a digital signal processor, a portable
computing device, a personal organizer, a device controller, and a
computational engine within an appliance. Cluster network 102 can
generally include any type of wire or wireless communication
channel capable of coupling together computing nodes. This
includes, but is not limited to, a local area network, a wide area
network, or a combination of networks.
Computing nodes 106 109 host a number of application components 110
117, which communicate with each other to service requests from
clients 121 123. Note that application components can include any
type of application (or portion of an application) that can execute
on computing nodes 106 109. During operation, resources within
computing nodes 106 109 provide a distributed event notification
mechanism that can be used by application components 110 117 to
coordinate interactions between application components 110 117.
This distributed event notification mechanism is described in more
detail below with reference to FIGS. 2 5.
Note that although the present invention is described in the
context of a highly available server 101, including multiple
computing nodes 106 109, the present invention is not meant to be
limited to such a system. In general, the present invention can be
applied to any type of computing system with multiple computing
nodes and is not meant to be limited to the specific highly
available server 101 illustrated in FIG. 1.
Computing Node
FIG. 2 illustrates a computing node 106 in accordance with an
embodiment of the present invention. Computing node 106 contains a
node operating system (OS) 206, which can generally include any
type of operating system for a computer system. Cluster operating
system (OS) 204 runs on top of node OS 206, and coordinates
interactions between computing nodes 106 109.
In one embodiment of the present invention, cluster OS 204 supports
failover operations to provide high availability for applications
running on computing nodes 106 109. In this embodiment, cluster OS
204 ensures that state information for an application is propagated
to persistent storage. In this way, if the application fails, a new
instance of the application can be automatically started by
retrieving the state information from persistent storage. Note that
the new instance of the application can be started on either the
same computing node or a different computing node. Moreover, the
failover operation generally takes place without significantly
interrupting ongoing operations associated with the
application.
Cluster OS provides an event application programming interface
(API) that can be used by application components 110 111 to receive
event notifications. More specifically, event API 202 enables
application components: to register to be notified of events; to
post events; and to and to receive notifications for events as is
described below with reference to FIGS. 3 5.
Event Forwarding Components
FIG. 3 illustrates components involved in the event forwarding
process in accordance with an embodiment of the present invention.
As is illustrated in FIG. 3, computing nodes 106 109 in the highly
available server 101 contain inter-node event forwarders (IEFs) 302
305, respectively. Each of these IEFs 302 305 receives events
generated locally on computing nodes 106 109 and automatically
communicates the events to all of the other IEFs as is illustrated
by the dashed lines in FIG. 3.
Computing node 107 also contains a highly available event forwarder
(HA-EF) 306, which is responsible for forwarding specific events to
clients that desire to be notified of the specific events. HA-EF
306 does this by receiving an event from IEF 303 on computing node
107 and then looking up the event in a cluster database 307 to
determine which clients desire to be notified of the event. HA-EF
306 then forwards the event to any clients, such as client 308,
that desire to be notified of the event.
Note that client 308 can be located within computing nodes 106 109.
For example, an application component 110 on computing node 106 can
be notified of a change in state of an application component 115 on
computing node 107. Client 308 can alternatively be located at a
remote client. For example, an application on client 121 can be
notified of state changes to a group of related application
components 110, 115 and 112 running on computing nodes, 106, 107
and 109, respectively.
Note that HA-EF 306 is "highly available." This means that if HA-EF
306 fails, a new instance of HA-EF 306 is automatically restarted,
possibly on a different computing node. Note that HA-EF 306 can be
restarted using client registration information stored within
cluster database 307. In one embodiment of the present invention,
when a new instance of HA-EF 306 is restarted, the new instance
asks for a snapshot of the event information from all of the other
nodes.
Also note that cluster database 307 is a fault-tolerant distributed
database that is stored in non-volatile storage associated with
computing nodes 106 109. In this way, the event registration
information will not be lost if one of the computing nodes 106 109
fails.
Registration Process
FIG. 4 is a flow chart illustrating the registration process for
event notification in accordance with an embodiment of the present
invention. The process starts when a client, such as client 308 in
FIG. 3, sends a registration request to HA-EF 306 (step 402). This
can involve sending the registration request to an IP address
associated with HA-EF 306. (Note that this IP address can be a
"highly-available" IP address that stays the same regardless of
which cluster node HA-EF 306 is running on.) This registration
request includes a callback address for client 308. For example,
the callback address can include an Internet Protocol (IP) address
and associated port number for client 308. The registration request
also includes a list of events that the client is interested in
being notified of.
Events in the list can include any type of events that can be
detected within computing nodes 106 109. For example, the events
can include cluster membership events, such as a node joining the
cluster or a node leaving the cluster. The events can also involve
applications. For example, the events can include: a state change
for an application (or an application component) running within the
distributed computing system, or a state change for a group of
related applications running within the distributed computing
system.
Note that a state change for an application (or application
component) can include: the application entering an on-line state;
the application entering an off-line state; the application
entering a degraded state, wherein the application is not
functioning efficiently; and the application entering a faulted
state, wherein the application is not functioning. The events can
also include state changes related to monitoring applications or
other system components, such as "monitoring started" and
"monitoring stopped." Also note that the present invention is not
limited to the types of events listed above. In general, any other
type of event associated with a computing node, such as timer
expiring or an interrupt occurring, can give rise to a
notification.
Upon receiving the registration request, HA-EF 306 records the
callback address of client 308 and the list of events in cluster
database 307 (step 404). HA-EF 306 then responds "success" to
client 308 and the registration process is complete (step 406).
After registering for an event, client 308 can simply disconnect
and does not need to maintain any connections to the cluster. When
an event of interest subsequently arrives, HA-EF 306 initiates a
connection to client 308 to deliver the event. Thus, client 308
does not need to do any maintenance, except for maintaining an open
listening socket.
Event Forwarding Process
FIG. 5 is a flow chart illustrating the process of forwarding an
event in accordance with an embodiment of the present invention.
This process starts when an event is generated at one of computing
nodes 106 109, for example computing node 106 (step 502). This
event generation may involve an application component (or operating
system component) posting the event through an event API on one of
the computing nodes. In one embodiment of the present invention,
events can be generated through the SOLARIS.TM. sysevent mechanism.
(SOLARIS is a registered trademark of SUN Microsystems, Inc. of
Santa Clara, Calif.)
Next, a local IEF 302 on computing node 106 receives the event and
forwards the event to the other IEFs 303 305 located on the other
computing nodes 107 109 (step 504). In one embodiment of the
present invention, the event is added to the sysevent queue in the
delivered nodes, which allows the event to be treated as if it was
generated locally (except that it is not again forwarded to other
nodes).
Next, HA-EF 306 receives the event and looks up an associated list
of clients in cluster database 307. This lookup can involve any
type of lookup structure that can efficiently lookup a set of
interested clients for a specific event. HA-EF 306 then forwards
the event to all of the clients in the list (step 506). This
completes the event notification process.
Note that the event notification process facilitates the
development of distributed applications because it allows
application components running on different computing nodes to be
informed of state changes in related application components without
having to exchange heartbeat messages or other status information
between the application components.
Also note that in many applications, it is important to guarantee a
total ordering of events. Hence if events are missed, it is
advantageous for subsequent events to indicate the total state of
the system, so that clients are not left with an incorrect view of
the event ordering.
Data Structure for the Event Lookup Process
In one embodiment of the present invention, the event lookup
process described in step 506 above involves an inverse mapping
operation that attempts to match an incoming event with a set of
client event registrations. More specifically, each incoming event
specifies a class and a sub-class for the event and a set of
name/value pairs associated with the event. The lookup process
matches the incoming event with client event registrations that
contain the same class and subclass and a subset of the name/value
pairs associated with the event.
For example, a given incoming event may be associated with
class="cluster," subclass="resource group state" and a number of
name/value pairs: {resource group name="foo"}; {node="node1"}; and
{state="online"}. This incoming event will match any client event
registration with the same class and subclass and that contains a
matching subset of the name/value pairs in the incoming event.
(Note that it is possible for a client event registration to
specify no name/value pairs, in which case any event with the same
class and sub-class will match the client event registration.)
FIG. 6 illustrates various data structures that facilitate the
inverse mapping operation in accordance with an embodiment of the
present invention. These data structures include a hash table 602,
which contains entries associated with a specific class, a specific
subclass and a specific name/value pair.
For example, hash table 602 includes entry 604, which is associated
with class1, subclass1 and name/value pair 1 (nv1). Hash table 602
also includes entry 606, which is associated with class 1, subclass
1 and name/value pair 2 (nv2). Hash table 602 additionally includes
entry 608, which is associated with class 1, subclass 1 and
name/value pair 3 (nv3).
Each hash table entry (604, 606 and 608) points to linked list of
pointers which point to corresponding event data structures. For
example, entry 604 in hash table 602 is associated with a linked
list containing pointers 610, 611 and 612, which point to event1
data structures 616, event2 data structure 617 and event3 data
structure 618, respectively. Entry 606 in hash table 602 similarly
points to a linked list containing pointers 613 and 614, which
point to event2 data structure 617 and event3 data structure 618,
respectively. Finally, entry 608 in hash table 602 points to a
linked list containing a single pointer 615, which points to event3
data structure 618.
Event data structures 616 618 represent specific client event
registrations. For example, in FIG. 6, a client associated with
client data structure 621 is registered to be notified of event1
and event2, which are associated with event1 data structure 616 and
event2 data structure 617, respectively. Event1 data structure 616
and event2 data structure 617 contain back pointers 652 and 655,
which point to client data structure 621, and client data structure
621 points to a list containing event1 data structure 616 and
event2 data structure 617.
Similarly, a client associated with client data structure 622 is
registered to be notified of event3, wherein event3 is associated
with event3 data structure 618. To keep track of these
associations, event3 data structure 618 contains a back pointer
658, which points to client data structure 622, and client data
structure 622 points to a list containing event3 data structure
618. Note that client data structures 621 and 622 are part of a
list of clients 620.
Each event is associated with a number of properties. In
particular, event1 is associated with class1, subclass1 and
name/value pair 1 (nv1). To keep track of this association, entry
604 in hash table 602 is associated with a pointer 612, which
references counter 650 within event1 data structure 616. This
allows a subsequent lookup into entry 604 to increment counter 650.
Event1 data structure 616 also contains a total 651, which
specifies the number of name/value pairs associated with the event.
In this case, total 651 is set to "one" because event1 data
structure 616 is only associated with a single name/value pair.
Whenever counter 650 is incremented, the resulting value is
compared against total 651. If the resulting value matches total
651, the associated client is placed in notification list 630, so
that the associated client will subsequently be notified of the
event.
Event 2 is similarly associated with class1, subclass1 and nv1.
However, event2 is also associated with name/value pair 2 (nv2).
Hence, counter 653 within event2 data structure 617 is referenced
by pointer 611 through entry 604 in hash table 602, and is also
referenced by pointer 614 through entry 606 in hash table 602. Note
that total 654 within event2 data structure 617 is set to the value
"two" because event2 data structure 617 is associated with two
name/value pairs, nv1 and nv2.
Finally event3 is associated with class1, subclass1, nv1, nv2 and
name/value pair 3 (nv3). Hence, counter 656 within event3 data
structure 618 is referenced by: pointer 610 through entry 604 in
hash table 602; pointer 613 through entry 606; and pointer 615
through entry 608. Note that total 657 within event3 data structure
618 is set to the value "three" because event3 data structure 618
is associated with three name/value pairs, nv1, nv2 and nv3.
FIG. 6 also includes a visited list 640, which keeps track of the
counters that have been incremented for an incoming event. This
allows the counters to be reset after the incoming event is
processed.
Process of Initializing Event Lookup Data Structures
FIG. 7 presents a flow chart illustrating the process of
initializing the lookup structure involved in the event lookup
process in accordance with an embodiment of the present invention.
The system starts by cycling through the client event
registrations. Upon accessing a specific client event registration
(step 702) the system creates a client data structure (such as
client data structure 621 in FIG. 6) if one does not already exist
(step 704). The system also creates an event data structure for
each client event registration, such as event1 data structure 616
in FIG. 6, if one does not already exist (step 706).
Next, for each name/value pair specified in the client event
registration, the system creates a hash key. For example, in FIG.
6, the hash key for entry 606 in hash table 602 is created from
class1, subclass1 and name/value pair1. The system uses this hash
key to perform a lookup in hash table 602. Note that this lookup
may involve creating a hash table entry for the hash key if an
entry does not exist. Next, the system adds a pointer from the hash
table entry to the event data structure so that subsequent lookups
using the same hash key can increment a counter in the event data
structure (step 708).
Note that the client event registrations may be received over time
as they are generated at the client computer systems during systems
operation. In this case, each additional client event registrations
is used to incrementally update the lookup structure.
Note that subsequent lookup operations involving the
above-described data structures do not require any time-consuming
string comparison operations; only fast hash table lookups and
pointer lookups are required.
Operations Involved in the Event Lookup Process
FIG. 8 presents a flow chart illustrating the event lookup process
in accordance with an embodiment of the present invention. Upon
receiving an event (step 802), the system processes a name/value
pair for the event (step 804). This involves generating a hash key
for the name/value pair and the associated class and subclass (step
806). The system uses this hash key to perform a hash lookup to
locate a corresponding hash table entry (step 808).
Next, the system follows an event pointer in the hash table entry
to locate an event data structure (step 810), and then increments a
counter in the event data structure (step 812). The system also
places a reference to the counter in visited list 640, so that the
counter can be reset after the event is processed. If a value in
the counter equals the total number of name/value pairs associated
with the event data structure, the system adds the associated
client to notification list 630 so that the client will be notified
of the event (step 814). Steps 810, 812 and 814 are repeated for
each event pointer in the hash table entry.
Next, if there are more name/value pair associated with the event,
the system returns to step 804 to process the next name/value pair
for the event. Otherwise, the system resets all of the counters in
visited list 640 (step 818). The system also sends event
notifications to all clients in visited list 640 and resets visited
list 640. At this point, the system is ready to process the next
event.
Example Lookup
For the exemplary set of client event registrations illustrated in
FIG. 6, suppose an incoming event has the following properties,
class1, subclass1, name1=value1 and name2=value2. Since there are
two name/value pairs (name1=value1 and name2=value2) for this
event, there are two possible hash keys
(class1:subclass1:name1=value1) and
(class1:subclass1:name2=value2). (In FIG. 6, note that "NV1"
represents name1=value1, "NV2" represents name2=value2, and "NV3"
represents name3=value3.)
The system first performs a lookup based on the first hash key
which returns entry 604 from hash table 602. Entry 604 points to
events 616 618. Next, the system increments counters for events 616
618 so that they contain the number one. Event1, which is
associated with event1 data structure 616, only requires one match,
so the associated client is placed on notification list 630. Event2
and event3, which are associated with event2 data structures 617
and event3 data structure 618, respectively, require more than one
match, so clients for event2 and event3 are not placed on
notification list 630 yet.
Next, the system performs a second lookup based on the second hash
key. This second lookup returns entry 606 from hash table 602,
which points to event2 data structures 617 and event3 data
structure 618. The system then increments counters 653 and 656 for
event2 data structure 617 and event3 data structure 618 so that
they contain the number two. Event2 only requires two matches, so
the associated client is placed on notification list 630. However,
event3 requires three matches, so the associated client for event3
is not put into notification list 630.
At this point, the lookup is complete, and the system sends
notifications to the clients in notification list 630 and then
clears notification list 630. The system refers to visited list 640
to clear all of the counters that have been incremented.
The foregoing descriptions of embodiments of the present invention
have been presented for purposes of illustration and description
only. They are not intended to be exhaustive or to limit the
present invention to the forms disclosed. Accordingly, many
modifications and variations will be apparent to practitioners
skilled in the art. Additionally, the above disclosure is not
intended to limit the present invention. The scope of the present
invention is defined by the appended claims.
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